Drilling devices wherein a drill bit is operated by a downhole motor, e.g., a positive displacement fluid motor or a turbine driven motor, are well known. In such motors the drill bit is rotated by a rotor which is turned by flow of fluid, e.g., a flow of drilling fluid through the motor.
U.S. Pat. No. 4,729,675 is directed to a bearing assembly for supporting a rotor drive shaft in a downhole motor. The device described in the '675 patent includes stacked bearings, and bearing sleeve members and springs. The sleeve members may be interchanged to change bearing loading according to the amount of upward or downward thrust imposed on the shaft during the drilling operation. The device described in the '675 patent contemplated thrust loading on a particular arrangement of bearings and sleeve from only one direction; i.e. if a reversal of the direction of loading was anticipated, the bearing assembly was reconfigured to prepare for the new demands on the tool.
Drilling practices have evolved, i.e. current drilling practice imposes higher thrust loads and cyclic, bidirectional axial loading on a downhole motor, to the point that the bearing configuration described in the '675 patent is now deficient in several respects, i.e. the bearing configuration is prone to failure due to broken or chipped balls, cracked springs and/or shattered bearing races.